Our research program will emphasize the following four lines of inquiry over the next three-year period: 1) a detailed description of the mechanism(s) of iron porphyrin substitution reactions with particular attention to a correlation of rates and pathways with porphyrin-ligand structure and properties 2) the pathways by which metalloporphyrins bond to serum proteins and, most particularly, the manner in which metalloporphyrins are donated by a "reservoir" protein (serum albumin) to a protein specifically evolved for porphyrin transport (hemopexin) 3) an investigation of the ways in which a protein environment influences the reactivity of metalloporphyrins and vice versa 4) measurement of the superoxide dismutase activities of metalloporphyrins and a determination of structure-function relationships for these species.